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Abstract.A comprehensive frequency analysis of 57 Tau, supposed only a static pulsational arrangement, is presented based on 54 nights of photometric data collected between 1981 and 1995 (althogether 232 hours). The presence of individual frequencies is confirmed by intercomparing four subsets of this data set, however, the uncertainties in data coming from the sparse nights and low signal weaken the conclusion on some results. The entire data base is then used to resolve closely spaced peaks. Twelve frequencies are indentified using this process. Further multisite observations are recommended to confirm the present frequency solution. Two periods, with a high probability of being real, are found in the low frequency domain. They are suggested to arise from binarity or g modes, as in γ Dor stars. Single unusual cycles, possessing large amplitude, or displaying asymmetry, have been localized. A coherent frequency at 29.83 c/d with variable amplitude was found. The nonstandard behaviour of the light variation indicates that nonlinear and/or nonstationary processes could be very important in the investigation of δ Scuti observations.

We present 83 new times of maximum light of the SX Phoenicis (SX Phe) star DY Pegasi (DY Peg), based mainly on our new time-series photometric observations from the years 2004–2008. Together with the times of maximum light in the literature, a comprehensive study of the O - C diagram with the data spanning over seven decades leads to a new general ephemeris formula and the determination of a new value of the updated period 0.072926187( ± 3)d. The available times of maximum light can be well modeled with either a triple linear fit, or a fit concerning a continuously increasing period change combined with the light-time effect of an orbital motion. On the contrary, the decreasing period hypothesis suggested by some previous investigators appears to be rejected. The frequency analyses of the data collected in 2004 and 2006 provide the radial pulsation frequency 13.713 c d -1 and its four harmonics. However, although extra powers were present around the reported secondary frequency 17.8 c d -1 in the Fourier transformations of the new data sets, its signal-to-noise ratios were too low to detect this frequency.

Abstract. -The observations of the MUSICOS 1992 campaign concerned three scientific programs, among which was the study of azimuthal structures in the wind and chromosphere of the pre-main sequence Herbig Ae star AB Aur. The He 15876 Â line of AB Aur, which is formed in the expanding chromosphere of this star, most probably in the innermost parts of its wind, was continuously monitored at a spectral resolution of 30000 for about 4 days. The line was discovered to be variable in a spectacular way, the profile changing from pure emission to a composite profile including a deep absorption component in the course of a few hours. In this paper we present strong clues that suggest a rotational modulation of the line, with a period corresponding to the stars rotation period of 32 hrs. We confirmed the covariation of several non-photospheric spectral lines, formed at very different radial distances of the star, which strengthens the idea that the variability is the signature of azimuthal structures in the wind of AB Aur, most probably due to magnetically confined streams or loops emanating from the stellar surface. We present the data collected during the MUSICOS 1992 campaign, but also a data set of the Hel D3 line obtained with FOE at KPNO during the years 1991-1994 and a series of IUE spectra containing the Mgllh&k UV lines obtained one month prior to the campaign. A thorough discussion of the possible interpretations of the spectacular variations of the He I 5876 Å line is presented.

The paper introduces the structure and working principles of the diesel-LNG electronic injection system. For a further experimental study, the author transforms a X6170ZC-19 diesel engine to a hybrid-fuel engine by installing this electronic injection system, and the load characteristics experiment of which testifies that: the diesel-LNG diesel engine can accurately measure the natural gas consumption and can thus control fuel consumption; it also possesses high replacement ratio. In addition, comparing to pure diesel engine, the hybrid-fuel engine has lower fuel consumption and thermal load, and a better performance in environment protection.